Tailorable Multifunctional Sensors for Structural Health Monitoring of Composite Structures

Fiber-reinforced composites (FRPs) have complex failure mechanisms; therefore, assessing the safety of composite structures of modern airplanes is essential to their projected future use in the aerospace industry. An FRP composite structure under service is prone to mechanical (e.g., strain and impact) and temperature changes that must be reliably monitored. In this study, conditions such as stress, impact, and temperature were applied to glass fiber-reinforced polymer (GFRP) composite coupons so that the multifunctionality of very thin layers of carbon nanostructure-based (carbon nanofibers, carbon black, and carbon nanotubes) piezoresistive sensors of various geometrical patterns (grid, star, and o-line) directly screen-printed on the surface of the GFRP composite can be evaluated. Results showed that depending on the monitored parameter, the piezoresistive response (sensitivity, gauge factor, and time response) of carbon nanomaterials differ, and the sensor's geometry influenced the sensor performance independent of the carbon nanostructure used. Results showed outstanding sensor performance values, with carbon black-based o-line and grid sensors exhibiting the highest gauge factor of 26 and 24, respectively, and carbon nanotubebased grid sensors displaying the highest temperature coefficient of resistance of -0.35%/°C. In conclusion, the developed sensors have the potential to be integrated as part of the structural health monitoring (SHM) system to sense various changes with compiled results, allowing broad flexibility in terms of material selection depending on the intended application.